I went to my local pet shop. They are are telling me I should use a Bak-Pak 2 Skimmer which has a wet/dry fiter built in to it. I already have a cansiter filter. This is on a 36 gallon tank. Does this sound right????

I feel like a quality skimmer is a great addition for most marine aquariums. Notice I said quality, lots of junk on the market, your research will lead to joy. The unit you are describing is somewhat unique in that it also has a wet dry filter, which is great for CONVERTING ammonia but also a nitrate factory, and depending on your goals this could be a problem for invertebrates. The trend these days is nutrient EXPORT vs. nutrient CONVERSION. The skimmer is designed to remove or EXPORT the organics before they are CONVERTED to nitrates. If my goal was removing DOC's and avoiding high nitrates, I would go for a quality skimmer and forget about the wet dry. Do read the link below from my archives:

SKIMMERS
The ones I see a lot of good comments on, here and other forums, are the Super Skimmer by Coralife, the Won Brothers line, the ASM line and of course the EuroReef brand. Be advised, these things are rarely "set it and forget it" gizmos, they can require cleaning, maintenance, adjusting, etc. As you have already seen many of the products on the market are worthless junk, choose wisely, see link below.
http://www.wetwebmedia.com/ca/cav1i1/protein_skimmer_impressions.htm_________________Keepin' marines happy for 25 years